CAN transceivers in current use as known from the existing art typically have two modes, an active mode for communication and a sleep mode, i.e. a power-saving idle state. The application program running on each CAN bus participant can set the desired operating mode, and the transceiver changes automatically from sleep mode to active mode as soon as it recognizes a dominant bit on the CAN bus. While the transceiver is in sleep mode, the rest of the CAN bus participant can be switched off and is then switched on again when the CAN transceiver changes to active mode. A selective putting to sleep and/or waking of individual transceivers and/or CAN bus participants via the CAN bus is not provided in currently existing art.
The necessity of minimizing the consumption of electrical energy in vehicles has given rise to the development goal of selectively switching off or putting to sleep individual CAN bus participants (i.e., as a rule control devices) and also selectively reawakening them. These control devices are not to wake up every time they recognize a dominant bit on the CAN bus, but rather only when they recognize a specific message or a specific signal sequence on the CAN bus.
Patent document DE 103 58 584 A1 discusses a two-stage method for decoding a wake identifier in the data field of a CAN message by counting edges in the message until the data field is reached, with subsequent decoding through pattern recognition. In this way, the CAN transceiver can be operated in four modes. In addition to the modes described above, there is an additional savings mode and an intermediate mode. From the sleep mode, the transceiver changes automatically to savings mode as soon as it recognizes a dominant bit on the CAN bus. In the savings mode, it acquires a signal property and changes to the intermediate mode when it recognizes, within a specified time span, a number of signal properties, e.g. edges. From the intermediate mode it changes to the active mode only as soon as it recognizes a particular pattern in the 8-byte-long data field of the CAN message, which it decodes according to a specific method for this purpose. The wake pattern is configured for each CAN transceiver. If the transceiver does not recognize the wake pattern in the message, it goes back into savings mode. In intermediate mode, the power consumption is only slightly higher than in savings mode; the rest of the CAN node can remain switched off.
In this way, CAN networks are possible having so-called partial network operation, in which individual nodes remain in the power-saving savings mode and are monitored, while the other nodes communicate via the CAN bus. The individual nodes can be selectively reawakened from savings mode by an individual CAN message, the wake message. This is called selective wakeup. A plurality of wake messages can also be configured for one node.
Patent document WO2006/003540 A1 discusses another method for recognizing wake signals in which the duration of successive dominant and recessive phases is compared, and from this in each case the information ‘1,’ ‘0,’ or ‘invalid’ is recognized. Here the continuous bitstream on the bus is read without taking into account the message format.